It has previously been proposed to make rotary milling cutters with helical cutter bits in such a manner that the cutter bits are replaceable. They are removable for replacement by fresh, newly sharpened cutter bits. The cutter element itself is formed of a generally cylindrical body with grooves therein into which the cutter bits can be inserted and then clamped in position. The cutter bits are generally helical. A helical milling cutter of this type is shown in U.S. Pat. No. 3,672,017, having helical cutter elements of identical size and shape which are inserted in a corresponding number of helically extending longitudinal grooves. The cutter bits are clamped therein. The seats for the cutter bits accurately match the shape of the cutter bits themselves. After use of the cutter, the bits become dull and can then be replaced with new bits having a sharp edge. The body of the milling cutter itself need not be changed.
It has also been proposed to make rotary helical milling cutters in such a manner that the cutter elements themselves can be reground and sharpened after use. The cutter plates, which are replaceable, after sharpening, are repositioned by placing of shims thereunder and by radially shifting the cutter bits by using screws and the like. The cutter bits are thereby shimmed and clamped outwardly to such an extent that the decrease in size of the bit itself, due to the sharpening by grinding, is effectively compensated. Since the cutter bits are helically twisted, however, radial shifting can be effected only in one of the many directions which the cutter bit itself has. Thus, shifting of the cutter bit on the milling cutter body will leave voids and gaps beneath the cutter bit and the rear seating surface of the body, or the associated side wall or axially extending helical groove. Consequently, the cutter bit will no longer bear with its entire rear surface against the rear groove of the milling cutter body itself but will be supported to some extent bridge-like over gaps. The bottom surfaces of the longitudinal groove and the lower limiting surface of the cutter bits also may have gaps and voids therebetween, of varying height, and not necessarily corresponding to the amount by which the reground cutter bit has been repositioned.
The cutter bits usually are made of very hard metal, for example tungsten carbide or the like, and are generally brittle. Thus, if the cutter bits do not bear with their rear surfaces against the body of the milling cutter throughout their full length, they have the tendency to break or snap in use, or already upon being clamped in position.